Time-limit circuit-controller.



No. 796,646. PATENTED AUG 8, 1905.

E. M. HEWLETT. TIME LIMIT CIRCUIT CONTROLLER.

APPLICATION FILED MAY 12, 1903.

INVENTOR: Edward M. Hewlett.

bLJ $112,131.

UNITEI) STATES PATENT OFFICE.

EDWARD M. HEWLETT, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TIIVlE-LIMIT CIRCUIT-CONTROLLER.

' Specification of Letters Patent.

Patented Aug'. 8, 1905.

Application filed May 12, 1903. Serial No. 156,773.

. Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Time-Limit Circuit Controllers, of which the following is a specification.

It is very often desired in controlling elec tric apparatus that the time of a required operation shall be delayed for a determinate interval after a change of condition occurs. For example, when a circuit is overtaxed with current it would occasion considerable annoyance if the circuit were always immediately opened, since the apparatus is not endangered by a brief interval of overload. Also when there is an accidental ground it is undesirable to open the circuit unless the ground be of an enduring character. For this reason there is often employed a device known as a time-limit device, which may act directly on mechanical operating devices or as a relay for an auxiliary operating-circuit, by which an organization is thrown into operation immediately on the occurrence of 'the dangerous condition, its parts being so related that after a definite and commonly re ulable .period, if the dangerous condition still persist, the endangered circuit will be opened.

The present invention relates to devices of this character. The result has usually been accomplished by means of gear-trains or systems of clockwork, which are started into operation on the occurrence of the dangerous condition. This method is objectionable from the fact that the clockwork requires attention and does not give a uniform time period for affecting the control-circuit, the time being shortened with increased tension of the spring.

My invention admits of a time-limit device of absolutely uniform period and of thorough reliability and simplicity of construction.

In carrying out the invention I employ a magnetic device responsive to the conditions of load in the control-circuit, the timing action being effected by means of a dash-pot of novel construction. The common structure of a dash-pot in which a piston sliding in a cylindrical shell is employed is objectionable for the reason that the wear of the rubbing parts will render the time interval variable and the entrance of dust will render it uncertain. If oil or other liquids be employed, there are troubles from leakage or heat. I avoid these difficulties by constructing a pot with a flexible diaphragm and a iston working against the outside of the iaphragm, a leak-valveof a fine degree of adjustment being provided to regulate the time of traverse of the piston. A pot of this characteris combined with an electromagnet, the winding of which is in circuit with or governed by the circuit to be controlled. By means ofa suitable valve a quick motion of the partslmay be established in one direction to permit prompt recovery when the removal of the dangerous condition in the control-circuit occurs. The movement of the parts effects the closure of an auxiliary or local circuit, which opens or otherwise changes the controlled circuit after a definite persistency of the dangerous conditions, or may act to directly trip a circuit-breaker. Considerable trouble has been experienced from the heat ing, erosion, and arcing of the contacts on relays of this kind. The operation of the time-limit device being slow in its nature gives rise to heating and burning when the contacts are just'being made or opened. This is particularly the case when the circuit controlled carries alternating currents by reason of the vibration due to the wave form 'of current.

, One feature of improvement in my device involves the correction of this trouble by the interposition between the controlling-magnet and the dash-pot of a spring or other elastically-yielding body in which the vibrations are absorbed and which also contributes to a snap break when the device recovers its nor mal position.

My invention embodies various more or less subordinate features of novelty in addition to the broader ones alreadyoutlined, which will be hereinafter more fully set forth and will be definitely indicated in the cla ms.

In the accompanying drawings, which illustrate a device embodying my improvements, Figure l is a sectional view of a time-limit breaker. Fig. 2 is a side elevation, and Fig. 3 a top plan view.

1 represents a magnet or solenoid coil which when the apparatus is in service is connected in the governed circuit. In order to increase the power of this magnet without interfering with its range of armature motion, it is ironclad, being housed within a castiron casing 2 of bell shape, the top of which is closed by an iron cover having a central projection 23 extending into the mouth of the coil. The coil is provided with a brass tubular lining, within which is guided a soft-iron core t. The core is adjustable within a tubular carrier 5 to permit regulation of the gap between its upper end and a brass plug 6, by which the carrier 5 is connected to the piston-rod 7. This piston-rod is guided in the iron cover of the magnet, the limit of motion being determined by the top of the rentrant projection 23. The rod 7 is connected with the piston of the dash-pot through a helical spring 8, this spring nesting in a countersunk recess on the lower part of the piston, against the top of which one end of the spring bears, the other end of the spring being pinned fast to the rod.

9 represents a cup-shaped structure which forms the shell of the dash-pot, being suported by a bracket 10, the foot of which is agged fast by screws to the magnet-cap. The mouth of the pot is covered by a flexible diaphragm 11, formed of kangaroo leather or other flexible air-tight material. The center of the leather diaphragm is secured air-tight to a convex piston 12, having a curvature to conform to the face of the cup or pet. The cup is shown as comparatively shallow, since no great length of movement is required. The edge of the leather is connected to the periphery of the pot by two ring springs 13 1,3, which nest in corresponding grooves and form an air-tight joint. In the top of the pot is a leak-valve 1 1, having a channel milled parallel to its axis on the outside to permit graduation of the time. This is preferably formed in one piece with the screw, indicated, and the parts may be locked in position when set by jam-nut 15. In practice it is found that a very line adjustment may be secured by this means. The leakage of air around the screw-thread is sufficient for a long time-limit adjustment. This may of course be controlled by a closer or easier lit of the screw. In the top of the pot is also mounted a ball-valve 16, provided with an air-duct 17, open to the atmosphere and normally covered by the ball, and another duct 18, communicating with the pot and opening into the closed chamber containing the ball.

19 19 represent the two contact-tips forming a bridging contact carried by the piston and adapted to cross connect two cooperating contact-springs 2O 20, mounted on a suitable insulatingsupport on the top of the magnet and provided with means by which connection may be cstabhshed with any suitable device for controlling the governed circuits. For example, it may lead to a trip-coil of a circuit-breaker to open the control-circuit at the required moment.

WVhile the dashpot herein described is primarily designed for use with a time-limit de vice, it will be evident that it may be employed in any class of service where a definite time interval is required and where constancy of the timing interval is important. Assuming that an instrument of this character is connected in an electric circuit wherein an unusually heavy current passes, the core 41 is drawn up into the magnet against the tension of the spring 8, compressing said spring. The motion of the core is arrested by engagementof the plug 6 with the projection 33, forming part of the cap. The spring 8 is therefore always put under the same strain irrespective oil the severity of the overload, assuming, of course, that the overload is of suflicient strength to operate the core. Thus the movement of the piston will be always the same-that is to say, the time in which the instrument acts will be the same. The reaction of the spring 8 then forces the piston upward, compressing the air in the inclosed chamber beneath the diaphragm, the speed of movement being dependent upon the rate of leakage of air from the valve, and as this may he graduated nicely by adjustment of the screw 1 1 the time maybe definitely fixed. After the predetermined range of movement has been effected the contact-springs 2O 20" are bridged bythe bridging contacts ll) 19", thereby closing an operating-circuit through the leads connected with these contacts.

The spring 8 serves several other important functions besides that of rendering the time of action constant under different loads. It prevents trembling of the contacts under the vibration due to alternations of current and their effect on the core, thereby preventing heating and arcing of the contacts when they are just at the point of closure. Besides this, when the circuit is opened and the controhmagnct 1 therefore deenergized the spring gives a sudden reaction, which effects a very rapid break at the contacts 19 1. 9 and 20 20, which are connected in a local circuit. The descending movement of the core is un obstructed, since air can enter behind the diaphragm through the ball-valve 16, the entering air lifting the ball and permitting a free reciprocating movement for the core. If the obstructing-abutment 3 be omitted, then the relay no longer remains constant in timelimit under varying load, since a heavier load will produce a stronger thrust on the dashpot piston, but the spring 8 is still useful in avoiding burning and arcing.

The calibration of the instrument may be varied by adjusting the core downwardly in the tube, as by turning the screw-plug 5,

which carries the core. This increases the gap and also varies the relation between the core and the solenoid. The solenoid l'may be fed directly from the control-circuit or through the instrumentality of inductive de vices, such as transformers, as is customar in governing alternating currents.

Adjustment of the core'in its carrying-tube varies the gap between the iron projection 3 and the top of the core. This has a very important function in permitting quick re covery in case an overload occurs and declines before the relay trips or opens the circuit. The promptness of the fall of the core on a definite fall of current depends upon the degree of saturation of the core and the length of air-gap in the magnetic circuit. Obviously, if adjustment is such that a small decline of current causes a great decrease of magnetic flux the core will respond more quickly than if the gap were short and the saturation high. The relations described permit the most sensitive condition to be readily found and fixed.

What I claim as new, and desire to secure by Letters Patent of the United States, is

1. A time-limit device comprising an opcrating-solenoid, a timing device to regulate the movement of the core, a stop to arrest motion at a determinate core position, and

means for varying the air-gap in the magnetic circuit when the core attains this position.

2. A time-limit device comprising a movable element, a fluid reservoir or container having a fluid-tight yielding wall adapted to be moved by said element, a leak-valve to predetermine the time-limit, and a valve to permit rapid recovery of the movable element after operation.

3. A time-limit device comprising a movable element, a flexible diaphragm and piston operated thereby, a pot, ring springs clamping said diaphra m to the rim of the pot, and an adjustable eak-opening to regulate the time-limit.

4. A time-limit device comprising a movable element, a timing device to regulate its speed of motion, and means for maintaining the thrust uniform on the movable element irrespective of the power applied.

5. A time-limit device comprising a movable element, a timing device to regulate its speed, a spring to determine the thrust, and means to limit the strain of the spring irrespective of the power applied to the movable element.

6. A time-limit device comprising a movable element, a control-magnet, a timing device, a spring for operating the timing device, and a stop to limit strain of the spring by the magnet.

7. A time-limit device comprising a movable element, a control-magnet, a dash-pot, a spring between the magnet-armature and dash-pot, and a fixed stop to limit strain of the spring and pressure on the movable element.

8. A timelimit device comprising a timing element, an operating-magnet, a local circuit closed after a predetermined movement of the movable element, and a spring between the magnet-armature and the movable element to reduce vibration of the localcircuit contacts.

9. A time-limit device comprising a timing device, an operating-magnet, a movable element, a spring between the movable element and thetiming device, a stop to limit strain on the spring, and means for adjusting the air-gap in the magnetic circuit in the attracted position of the magnet-armature.

10. A time-limit device comprising a solenoid, a dash-pot, a piston therefor connected with the solenoid-core, and a spring between the core and piston.

In witness whereof I have hereunto set my hand this 11th day of May, 1903.

EDWARD M. HEWLETT.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD. 

